(1) Field of the Invention
The present invention relates, in general, to an ink jet head, and in particular, to an ink jet head including an ink circulating passage way therein.
(2) Description of the Related Art
In recent years, printers on which an ink jet head is mounted to eject an ink droplet to record an image on a medium are widely popularized in various fields including an industry, a home appliance, and so on. Since the ink jet head readily realizes images in grey scale and in color and has its low running cost the prospect for the future thereof is remarkable.
In the field of an ink jet printer, a Drop-On-Demand (D-O-D) ink jet head is currently a major one.
Japanese Laid-open patent application (KOKAI) PH11-207972 discloses a D-O-D ink jet head comprising a pressure chamber connected to a nozzle in a fluid communication to eject an ink droplet from the nozzle. The pressure chamber is formed of a nozzle plate having the nozzle, a top plate, and a side wall and bottom surface shaped on a piezoelectric material. The side wall is plated with nickel to form an electrode to apply an ink ejection pulse thereto and is deformed to generate pressure to eject the ink droplet when the pulse is applied. The sidewall functions as an actuator for ejecting ink. When air intake from the nozzle accidentally occurs in the operation of the ink jet head and thus a bubble is formed, the bubble dumps the pressure for ejecting ink in the pressure chamber even if the ink ejection pulse is applied to the electrode to deform the actuator. Therefore the ink jet head poses failure of ink ejection upon the air intake. Besides, in case that a waste or a foreign matter remains in a process of manufacturing the ink jet head, or ink includes a foreign matter, the nozzle occasionally clogs with the waste or the foreign matter, posing ejection failure. Furthermore, repetition of applying the ink ejection pulse causes the actuator to generate beat slightly, resulting in lowering viscosity of ink in the pressure chamber. Since characteristic of the ink ejection is changed by the variation of the viscosity, the ink jet head still poses the other problem that quality of printed characters and images is made inconsistent.
International Laid-open patent application (HYO) 2002-520289 also discloses a D-O-D ink jet head. In the publication, described in detail is a manufacturing method of the ink jet head in which a plurality of ink channels are formed on two rows respectively, each being made of a laminated, piezoelectric material.
Japanese Laid-open patent application (KOKAI) P2001-162795 discloses an ink jet head provided with a circulation system for circulating ink in an ink channel in order to prevent a nozzle from clogging with foreign matter, ink ejection characteristic from deteriorating due to air intake, and viscosity of ink from decreasing due to heat generated by repetition of deformation of a piezoelectric material.
To form the circulation system, a dedicated pump is employed in an outside of the ink jet head. Therefore, a controller for controlling the pump and a dedicated space in which the pump is set are needed in an ink jet printer. Besides the circulation system comprises a plurality of elements including a main ink tank, the dedicated pump, a filter, a relay tank, an ink tube fluidly communicating one of the elements with the other, and a connector joining the tube with one of the elements. Thus, a complicated management of the elements and a periodic maintenance are required to keep the system work well. Furthermore, since the plural tubes are needed to fluidly communicate between respective elements in the system, a lot of unavailable ink remains in the tubes as a waste ink.